The invention disclosed herein relates generally to semiconductor pressure sensing apparatus, and more particularly to such apparatus employing a piezoresistive stress sensitive element mounted in a low cost housing employing premolded elastomeric seals, one of which is electrically conductive.
It is well known to package piezoresistive stress sensitive elements so that they are adapted to sense fluid pressure. In order to obtain an output indicative of fluid pressure, such a stress sensitive element must be interfaced with other structure in at least two respects which may have significant effects on the output of the element. Specifically, the element must be mechanically supported and a fluid tight joint must be provided between the element and the support structure to enable fluid pressures to produce a force differential between different portions (typically opposite sides) of the element.
An example of such a pressure transducer is seen in U.S. Pat. No. 4,656,454 issued to M. Rosenberger on Apr. 7, 1987. The transducer in U.S. Pat. No. 4,656,454 shows a three piece housing enclosing a stress sensitive diaphragm and two elastomeric seals. The diaphragm is compressed between the two elastomeric seals and ports on either end of the transducer to allow the pressure into the housing to be measured. Piezoresistors on the diaphragm are used in detecting pressure changes. Electrical connections are made to the diaphragm by bonding electrical jumpers onto the conductive regions of the diaphragm. These electrical jumpers are also welded to electrical means which carry current to the outside of the housing. After the electrical connections are made the three pieces of the housing are then ultrasonically welded together.
The applicant has devised a unique piezoresistive pressure transducer design utilizing a low cost housing and premolded elastomeric seals, which design simplifies the assembly process by eliminating the need to bond electrical connections or ultrasonically weld housing pieces together.